As disk drive devices, devices using various types of recording disks such as optical disks, magnetooptical disks, or flexible magnetic disks are known. Among those, the hard disk drives (HDD) have been widely prevalent as storage devices for computers, and become one of the essential storage devices in the present computer systems. Further, the usage of the HDD is not limited to the computer systems, but is increasingly growing to, for example, moving image recording/reproducing devices, car navigation systems, mobile phones, or removable memories used in digital cameras or the like because of the superior characteristics.
The magnetic disk used in the HDD is provided with a plurality of data tracks and servo tracks formed concentrically. The servo track includes a plurality of servo data (servo patterns) distant from each other in the circumferential direction. User data is recorded in each area between servo sectors. By a head element section as a thin film element accessing a desired area (address) in accordance with the servo data, writing of the user data or retrieval of the user data can be performed.
Each servo pattern (in the present specification, this is referred to as a product servo pattern) is composed of a cylinder ID, a sector number, a burst pattern, and so on. The cylinder ID represents a track address, and the sector number represents a sector address in the track. The burst pattern includes relative position information of the magnetic head with respect to the track.
As described above, the product servo patterns are formed in each of the tracks distant from each other in the circumferential direction as a plurality of sectors. Each of the product servo patterns existing in the same position in the circumferential direction, namely having the same sector numbers is uniform in the position (phase) in the circumferential direction throughout the entire tracks. The product servo patterns are written on the magnetic disk in a factory before the HDD is shipped as a product. Conventional writing of the product servo pattern is performed using a servo writer as an external device. The HDD is mounted on the servo writer, and the servo writer positions the head in the HDD by a positioner (an external positioning mechanism) to write the product servo patterns generated by a product servo pattern generation circuit on the magnetic disk.
Presently, the product servo pattern writing process (servo track write (STW)) has a principal place in the manufacturing cost of the HDD. Especially in recent years, competition of the HDD in increasing capacity has intensified, resulting in the advancement of increases in tracks per inch (TPI). By increasing the TPI, the number of tracks increases, and the track width (track pitch) becomes smaller. These advances increase the STW time and also increase the high precision of the servo writer, thus causing increase in the STW cost. As such, there is a need for reducing the cost of the servo writer, shortening of the STW time, and so on.
As one measure of solving the above problems, self-servo-writing (SSW) has been proposed. In contrast to the conventional STW, in the SSW only the mechanical mechanism of the HDD itself is used, and a spindle motor (SPM) and a voice coil motor (VCM) in the HDD are controlled from an external circuit to write the product servo patterns using the external circuit. Thus, the cost reduction of the servo writer is achieved.
In the SSW, utilizing that the read element and the write element of the head element section are different in the positions in the radial direction (referred to as a read/write offset, in the present specification), positioning of the head element section is performed while the read element is reading the patterns already written in the inner circumferential side or the outer circumferential side, and the write element writes new patterns on the desired track the read/write offset distant therefrom. In the SSW, in addition to the product servo patterns, other patterns are written on the recording surface, and head positioning control and timing control are performed using the patterns.
Typically, the HDD has a plurality of recording surfaces, a plurality of head element sections each corresponding to the respective one of the recording surfaces, and an actuator for supporting the plurality of element sections. In the SSW, the patterns on the recording surface are read using one head element section (referred to as a propagation head in the present specification) selected from the plurality of head element sections, and the actuator is controlled using the signal of the patterns thus read, thereby performing positioning of the plurality of head element sections. In the positioned state, the patterns are simultaneously written on each of the recording surfaces by all of the head element sections.
In writing the product servo patterns, it is important to accurately position the head element section to the desired positions. It should be noted that although differing from the SSW, Japanese Patent Publication No. 11-45528 (“patent document 1”), for example, discloses that, in order for writing the servo information on the magnetic disk medium with high accuracy, a convexoconcave pattern is formed on the reverse side of the magnetic disk, and positioning of the head is performed by reading out the pattern.
In writing the product servo patterns by the SSW, it is important to write the patterns for each track with a desired track pitch. One of the measures therefor is to actually read the written patterns to compare the read values with previously determined reference values. By performing the position control of the head so that the measured values correspond to the reference values, the track pitch is controlled. Thus, the track pitch can be made to correspond to a desired value.
Specifically, in the SSW, function values of the read amplitudes of the patterns in three tracks adjacent to each other are calculated to move the head so that the function values correspond to the previously determined reference values. The reference values can be determined by writing ideal patterns on the HDD, which are designed uniformly, using the rotary positioner and then actually measuring the function values of the patterns.
The track pitch has a different value for every head element section. This is because the track pitch varies in accordance with the read width or the write width in addition to the reference values. In servo writing, depending on the design, there are some cases in which it is desirable to write the product servo patterns with a specific pitch regardless of the head. Further, in the actual SSW, variations among products exist. Therefore, in some products, the track pitch of the product servo patterns is substantially shifted from the desired value.